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Date
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

I agree that there are lots of contributors to overall uncertainty. However, I don't think a bias inductor is used to feed the diode with the correct current.?
?
The HPJournal from April 1983 gives the internal circuit for the 346B and this shows how the diode is matched using some resistors and a stub. I assume the 346A is the same but with a larger value attenuator at the output.
?
Looking at my old notes, I worked out that there is something like a 16dB attenuator at the tip of the 346A noise source and the blocking capacitor must be something like 1200pF.? I worked this out from a 1 port measurement of the 346A and I compared this to a model based on what is inside the 346 noise sources. Based on my findings, I think the coupling cap is something like 1200pF in my 346A but this may vary across device to device. I also worked out that the equivalent resistance of the diode and the matching resistors was about 44 ohms for my 346A.
Re: Solder Flux

 

It *IS* possible to solder without flux, using hydrogen in a carrier gas, but it requires a high enough temperature for the hydrogen to reduce surface oxides, and a relatively clean (thin oxide) surface.

There is lower flammability limit to consider, as well as whether the hydrogen might be a problem. I wouldn’t choose to use forming gas to seal a crystal can, for example.
?
One might use sputtered gold surfaces devoid of oxides, freshly plasma cleaned, a gold tin solder preform and a GaAs laser diode chip vapor phase cleaned, and want a reducing rather than inert carrier gas, when cleaning flux residue becomes infeasible.
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

Yes, I had a digital noise generator in mind. It is a rather simple circuit.
The HP 3561A (and later models) dynamic signal analyzer has such a source, and uses it for various measurements. HP3561 only goes up to 100kHz, but with modern chips, 10MHz would be easy.
10MHz is in the "oscilloscope range", so you are not limited to GHz techniques. Of course, you could also make a (zener) diode noise source and calibrate it (after some amplification) with a HP3400, or a modern scope, with built in RMS calculation. Exact amounts of amplification up to 10MHz are also no problem with modern chips.
Most modern AWGs can also produce noise at least up to 10MHz. You would need some attenuation to get down to HP364 levels, but attenuation is also easy at 10MHz.
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

I’m probably restating the obvious, but more is more happening than just the VSWR. You have the DC block characteristics to consider, the noise diode mismatch uncertainty, and any effects related to the diode bias supply. A conical inductor might be good to 50GHz, but the might not work well at 1MHz, shorting some of the noise output to the bias supply (or allowing power supply, stray RF or other noise into the diode).
?
And all of that is on top of the attenuator not having constant attenuation vs frequency.
Re: Solder Flux

 

I suppose because sometimes a more aggressive flux is necessary
to solve a certain problem.

I guarantee that if you don't use a flux when soldering your
electronics assemblies, you aren't making good solder joints.

It pays to keep an open mind.

-Chuck Harris


On Fri, 18 Oct 2024 11:38:40 -0700 "Frank Mashockie"
<fmashockie@...> wrote:
This is a pretty silly argument to make.? As Roy says, many chemicals
are hygroscopic including zinc chloride.? They absorb water readily
through water vapor in the air.? And that is how zinc chloride can
become acidic.

I'm sure it is a mistake we've all made before - using flux on
electronics.? But there are so many readily available fluxes for
different applications, I'm not sure why you'd make an argument for
using it now.
Re: Solder Flux

 

Eventually, the water will boil off, long before solder reaches its melting point.
?
I’ve never thought to ask anyone, but:
?
Does a similar process happen to oxide deposits?
?
Does the molten zinc chloride prevent surface oxides from re-forming?
?
Are some of the reaction products soluble in the molten zinc chloride?
?
Are there other flux components that carry out one or more of the above roles?
?
Re: Solder Flux

 

Zinc chloride fluxes are used for? brazing to bind two metals together due to the hydrochloric acid formed during hydrolysis which occurs when the flux is heated.? The HCl reacts with the metal oxide layer of the metal.? Here's a series of reactions with iron sulfate:
?
ZnCl2 + 2H2O > Zn(OH)2 + 2HCl
FeS + 2HCl > FeCl2 + H2S
ZnCl2 + H2S > ZnS + HCl
?
Now most of the HCl is a gaseous product, but you can see that the presence of zinc chloride continues to reduce the by-products of the initial reaction with the metal oxide layer.? It doesn't matter that the ZnCl2 is neutral under ambient conditions.? Because the process of heating it will create acidic byproducts like HCl.??
?
?
Re: Solder Flux

 

Citric acid. For acetic acid you need vinegar.

On 10/18/2024 9:38 AM, 搁别苍é别 wrote:
IIRC lemon juice is mild acetic acid
搁别苍é别
On 10/18/24 6:26 AM, Jim Ford via groups.io wrote:
Thanks, Chuck.? I've forgotten much of my chemistry since I switched majors from biochemistry to EE about 40 years ago.? IIRC, fluxes come
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
Re: Solder Flux

 

I am under the impression that KFBK in Sacremento used balanced dipole vertical antennas. Might be wrong about this. A center fed vertical does not need a ground system.

On 10/18/2024 9:31 AM, Michael A. Terrell wrote:
No. I've only wrked on Comark, Gates and RCA TV transmitters, butt I received the salvage of a 5KW Channel 8 NTSC tranmitter from Vietnam, after it was shot up by the enemy, and the engineers were killed I had a similar transmitter at Ft Greely. but it didn't have the two amplifer cabinets. That Aural fiinal would have been great for a Two Meter repeater!
The RCA used water cooled power tetrodes that were designed for just the TTU-265 series of UHF ransmitters.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

In case there are still any doubts about the low frequency VSWR of the 346A see below for a measurement of mine from 300kHz to 1GHz using an E5071B VNA and a 4431B-600006 Ecal module.
?
I know from experience that all of the 346A noise sources at work are very similar to this. I recall that the worst one had a VSWR of about 1.02:1 across 10MHz to about 500MHz. I don't think the VSWR was any worse than about 1.06:1 on any of them below 1MHz.
?
Below 1MHz, I think the VSWR will be flat at about 1.05:1 right down to VLF because the loss of the output attenuator will define this worst case VSWR at LF.
?
?
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

Now you have me curious; I just ran across a 346B in the lab at work this morning.? When I get back from lunch, I'll go check the date code.? ? Jim


On Fri, Oct 18, 2024 at 11:36 AM, jmr via groups.io
<jmrhzu@...> wrote:
It looks like my 346A can be used down to about 2MHz with good results. This may not be the case with all 346A noise sources though, especially if they are using different diodes for the newer noise sources.
?
Over the weekend, I could try and explore below 2MHz but I feel this is fairly pointless with my 346A as the ENR drops rapidly below 2MHz. However, it may be interesting to see how far down the PSA analyser can operate when I use the Noisecom noise source.
?
Both are meant to work down to 200kHz. Regardless of the result, I don't see this as a practical or reliable means to measure noise figure at such low frequencies.? I don't know if the BFR91 test amplifier can maintain a flat noise figure down below 2MHz. At some point it will start to show an increase in noise figure. I could also test a common gate JFET amplifier (with a BJT second stage) as this should hopefully show low 1/f noise and flat gain from maybe 30MHz down to very low frequencies. I just need to find it...
Re: An update on sponsoring the group.

 

Although a coworker was just telling me the other day that he knew a guy who had a border collie and several cats.? The dog would literally herd the cats!? So it is possible after all.? ? ?Jim Ford, Laguna Hills, California, USA?


On Fri, Oct 18, 2024 at 9:44 AM, Radu Bogdan Dicher
<vondicher@...> wrote:
Herding cats sometimes, it feels like... :)
Radu.?

On Fri, Oct 18, 2024 at 9:37?AM John via <jphutch60bj=gmail.com@groups.io> wrote:

David -

Thanks for the update and taking on the job of herding? heading up the group? ;-}


On 10/17/2024 7:31 PM, Dr. David Kirkby, Kirkby Microwave Ltd via wrote:
I posted a link earlier today requesting that people that had not sponsored the group before could consider doing so by denoting $5. My post seems to have raised a lot of concerns and emails, so I want to explain what happened.?
?
I know many people wanted to donate, but I don’t want to build up a big piggy bank of money to which we have no access. If folded we would have no access to the money. It’s non-refundable. So I'd rather have enough money to cover fees, but not an excessive amount. Hence I requested donations were only $5, and only if you had not already donated.
?
IMHO have been very fair, and our fees for the group have been fixed at $110/year, despite new groups getting less facilities paying $220/year. Groups dot io seem to be keeping the fees constant - they are not rising inline with inflation. We are considered a legacy group.

We had got enough money to cover the fees within 20 minutes, of my post, so I disabled the sponsor function. I have received a lot of private emails, mentions on here, and even a complaint about the way it was handled, so I thought I'd try to clarify why I did it the way I did, and how? you can usefully donate to a charity if you want to.

Firstly, the link that ended in /sponsor is created and destroyed by automatically, depending upon whether I enable the sponsorship feature. So I could not, ?as someone suggested, put a custom message. Those of you who tried donating later got a 404 error. Next time I will look into creating a custom message, which itself has a link to the sponsor, but warns that unless you are quick, you will likely not be able to donate.

If anyone wanted to donate, but was unable to, then please consider donating to one of the following charities. All want payment in UK pounds (GBP), but PayPal, a credit or debit card will just convert whatever you donate to your own currency.
?
If you don't want to deal in GBP, then you can send whatever currency you want to my personal PayPal address (drkirkby@...), and I will ensure it gets to the charity of your choosing. Please do not send to my business email address drkirkby@....

I put below in alphabetical order, a suggested list of UK charities. I know some people like donating to small charities. The third in the list is 100% voluntary, with zero employees. The fourth in the list is very small.? The other charities are better known, and bigger.
?
1) Cat’s Protection League
?
2) Dog's Trust
?
3) German Shepherd Dog Rescue (100% voluntary, zero employees).
(Declared conflict of interest, I own a German Shepherd)
?
4) Girlguiding (A small charity, but it does have paid employees)
This helps? young girls develop new skills and build self-confidence.
?
5) Open University
This provides education, including degrees. The courses are very high quality, but funding is tight.
?
A lot of material is made freely available too.
(Declared conflict of interest, I'm currently doing a BSc (honors) degree in mathematics at the Open University)
?
6) Royal Society for the Prevention of Cruelty to Animals (RSPCA)
?
?
?
Re: Solder Flux

 

This is a pretty silly argument to make.? As Roy says, many chemicals are hygroscopic including zinc chloride.? They absorb water readily through water vapor in the air.? And that is how zinc chloride can become acidic.??
?
I'm sure it is a mistake we've all made before - using flux on electronics.? But there are so many readily available fluxes for different applications, I'm not sure why you'd make an argument for using it now.
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

It looks like my 346A can be used down to about 2MHz with good results. This may not be the case with all 346A noise sources though, especially if they are using different diodes for the newer noise sources.
?
Over the weekend, I could try and explore below 2MHz but I feel this is fairly pointless with my 346A as the ENR drops rapidly below 2MHz. However, it may be interesting to see how far down the PSA analyser can operate when I use the Noisecom noise source.
?
Both are meant to work down to 200kHz. Regardless of the result, I don't see this as a practical or reliable means to measure noise figure at such low frequencies.? I don't know if the BFR91 test amplifier can maintain a flat noise figure down below 2MHz. At some point it will start to show an increase in noise figure. I could also test a common gate JFET amplifier (with a BJT second stage) as this should hopefully show low 1/f noise and flat gain from maybe 30MHz down to very low frequencies. I just need to find it...
Re: HP 346A Noise Source Below 10 MHz #file-notice

 

I dug out my precision analyser preamp (homebrew) and used this instead of using the internal preamp in the PSA analyser. My preamp has ultra low VSWR and a 2.8dB noise figure across a few MHz up to about 1GHz. The combination of the low VSWR and lower noise figure should minimise the measurement uncertainty when using the 346A noise source. See below for a fresh measurement of the BFR91 amplifier using my preamp inline with the PSA analyser.
?
?
?
This has no averaging but you can see how much cleaner the traces are when using my external preamp. I also measured the amplifier on a 2 port VNA after an Ecal calibration at -25dBm source power.
?
?
You can see that the gain is very flat at 12.5dB across 300kHz to over 50MHz. This agrees with the gain measurement using the 346A noise source and the PSA analyser.
?
My external preamp was designed to have very low VSWR from 1MHz to 500MHz and a sub 3dB noise figure. It also has very flat gain across this range although this is less important.
?
?
You can see the input VSWR of my precision preamp is ultra low across 1MHz to 500MHz.??
?
?
?
This plot shows how flat the gain of the external precision preamp is. It was designed to act as a precision wideband amplifier to use for instrumentation and you can see there is no passband ripple and the VSWR is impressively low. The noise figure is a flat 2.8dB from a few MHz to well over 500MHz. The noise figure creeps up slightly down at 1MHz, but only by a small amount.?
?
It really helps to minimise measurement uncertainty when doing noise figure measurements with the 346A and PSA analyser.
?
Despite all this, I can't guarantee how accurate the subsequent noise figure results are below 10MHz for the BFR93 test amplifier, but if I assume the gain and noise figure is flat with frequency down to 2MHz, then it looks like I can assume high confidence in the results I've achieved. I've taken reasonable steps to minimise measurement uncertainty.
?
It would be interesting to see how others would approach this task and what results they achieved. Because the noise performance of the 346A isn't specified below 10MHz then it may be the case that there could be differences (between various 346A devices) in how flat the noise output is below 10MHz. I've got access to about eight 346A noise sources at work (but sadly no 346B) so I could maybe ask to borrow them and test them one by one? Some already have a fairly low ENR at 10MHz of only 5.0dB. I've been using them at work for about 20 years and I think they are are all 2004 (44) date code devices.
?
My 346A here at home has a 1993 date code.
?
?
?
?
?
?
?
?
?
Re: Solder Flux

 

Something over 65 years ago I helped? install an RCA UHF transmitter.? RCA furnished a liquid flux, I think they called Kempane or something like that.? It came in a bottle with a brush and was used for soft soldering flanges on large copper transmission lines with a torch.? It worked very well.? In years since I wished I had some for soft-soldering waveguide flanges.? Is there a present day generic equivalent?
?
Bruce, KG6OJI
Re: Solder Flux

 

No, but I knew some engineers from that area, and often went to the Cincinnati Hamfest since I lived in Middletown.

I often had them hanging around my tables, discussing the stations where they worked. One was an engeer for the eductaional stations in Kenty when I first knew him. I moslly dealt n used test equip,ent, and some broardcast equipment. The only thing let from that era is a Scully 280 record amplifier..??

I worked in stations in Alaka, and Florida

On Fri, Oct 18, 2024 at 1:31?PM Hugh Gilbert via <gilbhugh=gmail.com@groups.io> wrote:
Michael, Your name sounds vaguely familiar to me. Have you ever worked for KET or KEWS or other facility here in Kentucky?
Re: Solder Flux

 

开云体育

yes, Thank you , note the correction I was moving the 25% vinegar jug this morning... it was on my mind.
搁别苍é别

On 10/18/24 10:10 AM, Dave Daniel via groups.io wrote:

The acid in lemon juice is citric acid. Vinegar contains acetic acid.

DaveD
KC0WJN

Thanks for all the fish.
==============================
All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994)
==============================

On Oct 18, 2024, at 12:38, 搁别苍é别 via groups.io <k6fsb.1@...> wrote:

? IIRC lemon juice is mild acetic acid
搁别苍é别

On 10/18/24 6:26 AM, Jim Ford via groups.io wrote:
Thanks, Chuck.? I've forgotten much of my chemistry since I switched majors from biochemistry to EE about 40 years ago.? IIRC, fluxes come in several classes, R for pure rosin - not activated, RMA for rosin mildly activated - a small amount of acid added, and RA for rosin activated - a relatively large amount of acid added.? Then there's the "acid" flux - no rosin at all, and as people have said, suitable for plumbing and not for electronics.? I had heard years ago that Hughes Aircraft (since split into Raytheon where I work and Boeing) was using lemon juice instead of rosin flux, but I haven't tried that.? ? ? ? Jim


On Fri, Oct 18, 2024 at 5:40 AM, Chuck Harris
Ok, let's talk about this.

It is true that the OP didn't mention whether he was using
a paste, or a liquid... just that what he was using had 27%
ZnCl.? If the other 73% is water, that would cause problems
all of its own... If it is 73% something else, perhaps not.

The pubchem listing you brought into this conversation must
be for an aqueous solution of ZnCl and water, or pH would
be undefined.

[pH == -log10(H+), or 14 - log10(OH-)]

It should be obvious that ZnCl has no water, just as the
NaCl in the shaker in your kitchen has no water.

A liquid solution of ZnCl in water would be very difficult
to handle in an electronic application. it would run
everywhere leading to the anecdotes that sprung up like
mushrooms on the mention of ZnCl as a flux...

About the only way liquid ZnCl flux could be used in
electronics work is dipping a lead in it before soldering.

Liquid ZnCl flux is mostly water and HCl, so it is bad
to even have around electronics equipment.

I inferred by the OP's use case, that he was talking
about the old fashioned ZnCl solder paste concoction
that has been used for decades in the assembly of
point-to-point soldered electronic equipment.

At this point in the conversation only he knows which of
us made the correct guess.

ZnCl is a compound that is neither an acid, nor a base.
It is neutral.? ZnCl in water is far more interesting.
It is also neither an acid, nor a base.? It is an ionic
solution of Zn+, Cl-, H+ and OH- ions all in a perfect
balance.

That said, it is impossible to say which +ions of the
ionic solution are "coupled" with which -ions, so a ZnCl
solution is at the same time comprised of:

H+ Cl-, Zn+ OH-, and H+ OH-

It looks as much like hydrochloric acid (a strong acid),
as it does like ZnCl (a neutral salt), as it does like
zinc hydroxide (a strong base).

The typical liquid ZnCl flux is not "killed".? It is left
a little spicy by not completely neutralizing the HCl with
ZnOH.

It is a ZnCl/HCl solution.

Rosin flux:

Rosin flux that is not activated, will do nothing to help
in soldering a joint made up of slightly oxidized copper
pieces.? The solder will ball up, never wetting the copper.

It may help in soldering a joint with clean metals, as it
will keep the oxygen in the air from reacting with the
hot copper.

To make such a joint, you would have to either freshly
sand the oxide off of the copper, or apply a scrubbing
action (to break up the oxides) with your soldering iron
tip.

To make soldering a little easier, manufacturers "activate"
the rosin to various degrees.? Activation is another word
for adding acid.? The acid combines with the oxide, puts
it into solution, where it floats to the surface of the
joint and sits relatively harmlessly until moisture from
the air gets involved.? Just as the ZnCl in solder paste
does.

-Chuck Harris

On Thu, 17 Oct 2024 13:40:47 -0700 "Robert G8RPI via groups.io"
<robert8rpi@...> wrote:
> Chuck said:
> "Come on guys, it really isn't that bad. ?The stuff he
> is talking about is a petroleum jelly based zinc chloride
> compound. ?Zinc Chloride is a killed acid. ?That means that
> they dissolve enough zinc into HCL that it can take no more,
> and is neutral pH.
> It is non-corrosive, and says so in bold red letters right
> on the can."
>
> Not according to
> who say "It
> is corrosive to metals" The key is in the "chloride". I don't know
> how you determined the OP had a jelly based flux as he didn't say.
> Not all flux is corrosive. Rosin flux is not. It does not have to be
> it works by excluding air (oxygen) from the hot joint. A solution fod
> zinc hloride is acidic with a PH of about 4. It is not suitable for
> electrical applications.
>
> Robert.
>
>
>
>
>








Re: Solder Flux

 

Michael, Your name sounds vaguely familiar to me. Have you ever worked for KET or KEWS or other facility here in Kentucky?
Re: Solder Flux

 

开云体育

The acid in lemon juice is citric acid. Vinegar contains acetic acid.

DaveD
KC0WJN

Thanks for all the fish.
==============================
All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994)
==============================

On Oct 18, 2024, at 12:38, 搁别苍é别 via groups.io <k6fsb.1@...> wrote:

? IIRC lemon juice is mild acetic acid
搁别苍é别

On 10/18/24 6:26 AM, Jim Ford via groups.io wrote:
Thanks, Chuck.? I've forgotten much of my chemistry since I switched majors from biochemistry to EE about 40 years ago.? IIRC, fluxes come in several classes, R for pure rosin - not activated, RMA for rosin mildly activated - a small amount of acid added, and RA for rosin activated - a relatively large amount of acid added.? Then there's the "acid" flux - no rosin at all, and as people have said, suitable for plumbing and not for electronics.? I had heard years ago that Hughes Aircraft (since split into Raytheon where I work and Boeing) was using lemon juice instead of rosin flux, but I haven't tried that.? ? ? ? Jim


On Fri, Oct 18, 2024 at 5:40 AM, Chuck Harris
Ok, let's talk about this.

It is true that the OP didn't mention whether he was using
a paste, or a liquid... just that what he was using had 27%
ZnCl.? If the other 73% is water, that would cause problems
all of its own... If it is 73% something else, perhaps not.

The pubchem listing you brought into this conversation must
be for an aqueous solution of ZnCl and water, or pH would
be undefined.

[pH == -log10(H+), or 14 - log10(OH-)]

It should be obvious that ZnCl has no water, just as the
NaCl in the shaker in your kitchen has no water.

A liquid solution of ZnCl in water would be very difficult
to handle in an electronic application. it would run
everywhere leading to the anecdotes that sprung up like
mushrooms on the mention of ZnCl as a flux...

About the only way liquid ZnCl flux could be used in
electronics work is dipping a lead in it before soldering.

Liquid ZnCl flux is mostly water and HCl, so it is bad
to even have around electronics equipment.

I inferred by the OP's use case, that he was talking
about the old fashioned ZnCl solder paste concoction
that has been used for decades in the assembly of
point-to-point soldered electronic equipment.

At this point in the conversation only he knows which of
us made the correct guess.

ZnCl is a compound that is neither an acid, nor a base.
It is neutral.? ZnCl in water is far more interesting.
It is also neither an acid, nor a base.? It is an ionic
solution of Zn+, Cl-, H+ and OH- ions all in a perfect
balance.

That said, it is impossible to say which +ions of the
ionic solution are "coupled" with which -ions, so a ZnCl
solution is at the same time comprised of:

H+ Cl-, Zn+ OH-, and H+ OH-

It looks as much like hydrochloric acid (a strong acid),
as it does like ZnCl (a neutral salt), as it does like
zinc hydroxide (a strong base).

The typical liquid ZnCl flux is not "killed".? It is left
a little spicy by not completely neutralizing the HCl with
ZnOH.

It is a ZnCl/HCl solution.

Rosin flux:

Rosin flux that is not activated, will do nothing to help
in soldering a joint made up of slightly oxidized copper
pieces.? The solder will ball up, never wetting the copper.

It may help in soldering a joint with clean metals, as it
will keep the oxygen in the air from reacting with the
hot copper.

To make such a joint, you would have to either freshly
sand the oxide off of the copper, or apply a scrubbing
action (to break up the oxides) with your soldering iron
tip.

To make soldering a little easier, manufacturers "activate"
the rosin to various degrees.? Activation is another word
for adding acid.? The acid combines with the oxide, puts
it into solution, where it floats to the surface of the
joint and sits relatively harmlessly until moisture from
the air gets involved.? Just as the ZnCl in solder paste
does.

-Chuck Harris

On Thu, 17 Oct 2024 13:40:47 -0700 "Robert G8RPI via groups.io"
<robert8rpi@...> wrote:
> Chuck said:
> "Come on guys, it really isn't that bad. ?The stuff he
> is talking about is a petroleum jelly based zinc chloride
> compound. ?Zinc Chloride is a killed acid. ?That means that
> they dissolve enough zinc into HCL that it can take no more,
> and is neutral pH.
> It is non-corrosive, and says so in bold red letters right
> on the can."
>
> Not according to
> who say "It
> is corrosive to metals" The key is in the "chloride". I don't know
> how you determined the OP had a jelly based flux as he didn't say.
> Not all flux is corrosive. Rosin flux is not. It does not have to be
> it works by excluding air (oxygen) from the hot joint. A solution fod
> zinc hloride is acidic with a PH of about 4. It is not suitable for
> electrical applications.
>
> Robert.
>
>
>
>
>







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